Hard Scouting Can Avert Loss From Stinkbugs, Bean Leaf Beetles
COLUMBIA, MO.
Missouri corn and soybean producers
should scout hard for brown sting bugs
and bean leaf beetles. Populations of
these pests are especially high in late-planted
fields and threaten major damage or yield loss
if not treated, said Wayne Bailey, University of
Missouri Extension entomologist.
Bean leaf beetles are inflicting heavy damage
to soybean plants in northern Missouri.
“Most reports are from areas
where soybean fields are few in
number and beetles have congregated
in those fields that have been
planted,” Bailey said.
“There’s high beetle numbers out
here, and it seems like they’re just
hitting newly planted beans,” said
Wayne Flanary, MU Extension
agronomist in Holt County in northwestern
Missouri. “I’ve seen this
damage in April or May with overwintering
populations, but because
of late planting they are attacking
newly planted soybeans. I’ve nev 1/4
inch long and can be tan, dark red,
pink, green or brown. Most have
black spots on the upper back, Bailey
said, and all bean leaf beetles
have a black triangle just behind their heads.
Adult beetles damage plants by chewing
holes in leaf surfaces. They typically do not
chew through larger leaf veins or ribs, Bailey
said, but late planting this year has favored
beetles and reduced soybean fields. “This year
we have high beetle numbers, which can totally
defoliate and often kill the seedlings.”
The economic threshold is five or more beetles
or one or more plants destroyed per row
foot, Bailey said. Many insecticides are labeled
for bean leaf beetles. Seed treatments also help
reduce their numbers.
“They’ll be around for a while, but they’re
pretty easy to kill,” he said.
Brown stinkbugs pose a serious risk to
seedling corn plants, but are harder to kill,
Bailey said. Northern and southwestern Missouri
have had the most damage so far, but
corn seedlings throughout the state are at risk.
Adult stinkbugs suck out plant juices, giving
the plants a twisted, stunted or shabby appearance.
“They typically damage 5 to 10 percent
of plants, but damage is much higher this
year,” Bailey said. “A lot of fields are at 25 percent
right now. In some cases they can damage
as much as 60 percent of plants.”
Stinkbugs may also damage the plant’s growing
point, he said. “This kind of damage results
in plants that may die rapidly. If the plant survives,
it can be stunted or produce a tiller
which is almost always a weed.”
Signs of damage often appear first along field
edges, but if unnoticed can spread throughout
the field. A good indicator of stinkbug damage
is the presence several oval holes located in a
line across the corn leaves as they grow out of
the whorl, Bailey said. A yellow border often
surrounds the holes.
Frequent scouting is essential to prevent
major economic loss, as feeding damage may
start 10 to 20 days before clear signs of twisting,
stunting, wilting or plant death appear.
“If you can find stinkbugs when they’re actively
feeding, you can knock their population
down, but any plants fed on will have problems.”
The economic threshold is one stinkbug
per row foot.
“When scouting, look near the base of the
plants, on foliage, at leaf nodes and in plant
whorls,” Bailey said. “The bugs hide low during
the day or when it’s windy.”
To treat, select a spray labeled for stinkbugs.
Make sure to get a positive stinkbug identification
first, as other insects such as wireworms
and billbugs can cause similar damage.
“If plants are stunted but survive, you can
come close to the original yield if conditions are
right,” he said.
Later in the season, green stinkbugs may
pose a problem for soybeans. For questions or
help identifying pest damage, contact your
local MU Extension office. Δ